Mercury is a heavy metal whose toxic effect is well known. Amalgams are alloys which contain relatively large quantities of Hg. Amalgam used in dental fillings contains about 50 percent by weight metallic Hg. Hg is released more or less continuously from the fillings in both vapor form and in the form of solution, as a result of the corrosion and the wear that occurs naturally in the oral cavity because of the abrasion between fillings and tooth surfaces, and also as a result of the pH of the saliva. The amount of Hg released will increase when the fillings are subjected to pronounced strain, particularly when chewing, for instance in conjunction with consuming different foodstuffs, and also when brushing the teeth, and may be more than 6-fold in cases such as these. This elevated Hg release will often not diminish until 40-50 minutes have lapsed after termination of this pronounced strain on the fillings. Mercury that is released in vapor form and in the form of a solution is taken up via the lungs or swallowed with saliva. Investigations have shown that the average daily absorption of mercury per person is about 3 -17 .mu.g ("Inorganic mercury", Environmental Health Criteria Document 118, WHO 1991). Although there is some controversy as to whether or not the ingestion of such quantities would regularly result in Hg-poisoning, there is no doubt that comparatively highly sensitive persons can be afflicted by these mercury levels. Dental personnel handling amalgam are also exposed to the mercury that is released during treatment, particularly when inserting new fillings and when polishing and drilling existing fillings. It has been found that on such occasions, the ambient air can have mercury concentration values as high as 50 .mu.g/m.sup.3 measured in the breathing zone (Langworth, S., et al. "Undersokningar av kvicksilverexponering och halsorisker forknippade med amalgamhantering"; Slutrapport Arbetsmiljofonden, 1989). These high levels can be compared with the professional hygienic level limit currently applied in Sweden, which is only 30 .mu.g/m.sup.3.
SE-B-463 189 describes a preparation for introduction into the oral cavity. The purpose of this preparation is to prevent the release of Hg and Hg vapor from dental amalgam fillings or to reduce reduce the extent of such release. The preparation contains sulphur in a free form, preferably in concentrations of 0.1 -0.01 percent by weight and in particle sizes in the range of 0.05 -0.01 mm. Although it is maintained in the patent specification that the preparation may be present in many different forms, the sole embodiments described with examples are toothpaste and chewing gum, wherein the sulphur grains have an average size of 0.025 mm. In the examples documented, the sulphur is present in concentrations of 0.005 -5 percent by weight. However, it is also anticipated that the preparation may be used in mouth washes, mouth sprays, abrading and polishing agents and as a coolant when using dental instruments. This would create considerable problems in practice, however. For instance, it is highly unlikely that a colloidal sulphur solution could be used in dental instrument washing liquids without the sulphur particles settling to form a sediment, with the subsequent risk of clogging valves and like devices. A corresponding clogging risk would also be likely in the case of a mouth spray. The use of colloidal sulphur in a mouth-washing agent would also appear impractical in view of the unavoidable sedimentation risk.
U.S. Pat No. 5,178,541 also describes preparations and methods for preventing release of Hg and Hg vapor. This document also discloses the use of sulphur in such preparations and methods. A protective layer may be formed over hardened amalgam surfaces by brushing with a toothpaste composition containing sulfur. Alternatively, surfaces of a tooth cavity can be coated with a lining composition containing sulfur before inserting the dental amalgam. Also, sulphur may be incorporated into setting compositions comprising a dental amalgam alloy. Nothing is disclosed about preparations that can be used when polishing and drilling existing fillings.
WO 88/05295 describes a composition which is intended to prevent poisoning as a result of the dissolution of Hg from amalgam fillings, this composition containing selenium iodide. Selenium compounds, however, are known to be highly toxic, a problem which can hardly be ignored in the present context.
Chemical Abstracts, Vol. 105, abstract number 185439c & Twardowska-Saucha: Br. J. Ind. Med. 1986, 43(9), 611 -14, discloses treatment of mercury poisoning of animals with methicillin or penicillamine. Nothing is revealed about any dental applications.
Thus, there exists a need for means which are effective in inhibiting the release of Hg and in rendering released Hg harmless and which are not encumbered with the aforesaid problems.